1. Field of the Invention
The present invention generally relates to an organic electro-luminescent (to be abbreviated as “EL” hereinafter) display device and a method for manufacturing such an organic EL display device and, more particularly, to a passive matrix organic EL display device for use in a large-scale display panel and a method for manufacturing the organic EL display device.
2. Description of the Prior Art
The organic EL device has attracted tremendous attention due to its advantages over other display devices. These advantages include a larger visual angle, shorter response time, a smaller dimension in thickness, lower power consumption, simpler fabrication, no need for backlighting, and the ability for light emitting in a full color range.
Please refer to FIG. 1, which a cross-sectional view showing the structure of an organic EL device in accordance with the prior art. The organic EL device is characterized in that a first electrode 13 is formed on a substrate 11, and on the first electrode 13 there are a light-emitting layer 17 comprising an organic layer, a second electrode 15 and a protective layer 19 formed by evaporation or sputtering in turn. Electrons and holes are injected from the first electrode 13 and the second electrode 15 and then recombined in the light-emitting layer 17 so as to excite the light-emitting material in the light-emitting layer 17 and emit light.
From the viewpoints of driving mechanism of organic EL devices, organic EL devices can be divided into two categories: the passive matrix organic EL device and the active matrix organic EL device. The passive matrix organic EL device has a simpler structure than the active matrix organic EL device, and there is neither a thin film transistor liquid crystal display (TFT-LCD) panel nor a color filter required. Therefore, the fabrication complexity as well as fabrication cost for the passive matrix organic EL device is much lower. However, in a large-scale display panel composed of passive matrix organic EL devices, the pixels are driven in proper sequence. Hence, a large current is required to be injected into the pixels in a very short time so as to prolong the light-emitting time of the pixels. This leads to a limited number of scanning lines and poor resolution insufficient for a large-scale display panel.
On the contrary, in a large-scale display panel composed of active matrix organic EL devices, a larger number of scanning lines are allowed and the resolution is improved for a large-scale display panel. However, the pixels are driven by using independent thin film transistor circuits and low-temperature poly-silicon TFT technology is required for manufacturing active matrix organic EL devices. In other words, the fabrication of active matrix organic EL devices is critical because the cost is increased due to considerable fabrication complexity and mass production is not yet achieved for low-temperature poly-silicon TFT technology. Therefore, the passive matrix organic EL device still plays the major role in the OELD-related industry.
Please refer to FIG. 2, which is a block circuit diagram showing conventional passive matrix organic EL devices combined as a unit display panel in accordance with the prior art. As shown in FIG. 2, the unit display panel 21 is composed of a plurality of data lines 235 formed of first electrodes (indicated by 13 in FIG. 1) of organic EL devices and a plurality of scanning lines 255 formed of second electrodes (indicated by 15 in FIG. 1) of the organic EL devices. All the data lines 235 and the scanning lines 255 are connected, respectively, to a corresponding column driver 23 and a corresponding raw driver 25, which are further connected to a central controller 27 that controls through the column driver 23 and the raw driver 25 so as to determine which pixel (as indicated by a “spot” in FIG. 2) to emit light.
In order to implement the unit display panel for possible application in practical cases, the industry has managed to combine a plurality of OELD unit display panels as a large-scale display panel 31. As shown in FIG. 3, which is a 2×2 display device composed of four OELD unit display panels. The data lines 335 and the scanning lines 355 for each unit display panel are connected, respectively, to a corresponding column driver 33A1˜33A4 and a corresponding raw driver 35B1˜35B4. Each of the column drivers 33A1˜33A4 and the raw drivers 35B1˜35B4 is further connected to a central controller 37 that controls through the column drivers 33A1˜33A4 and the raw drivers 35B1˜35B4 so as to determine which pixel (as indicated by a “spot” in FIG. 3) to emit light. Even though this structure has a relatively larger size, the data lines 335 and the scanning lines 355 for each unit display panel have to be directly connected to the corresponding column driver 33A1˜33A4 and the corresponding raw driver 35B1˜35B4, respectively. Therefore, such a structure is only applicable as a 2×2 display device. In other words, a 2×3 or larger display device can not be implemented, because any unit display panel on the third column or the third raw has no corresponding column driver or corresponding raw driver to be connected to through the data lines or the scanning lines. Accordingly, such a passive matrix OELD display device has a size limit that cannot be further increased.
Therefore, there is need in providing a passive matrix organic EL display device and a method for manufacturing such an organic EL display device.